Why is my Cycles Smoke is disappearing in render?
This is because the max steps + step size is limiting the maximum distance volume rays are allowed to travel to a distance smaller than the total width of your domain.

Your domain is over 350 meters wide in the shortest axis. With the current settings in Render settings > Volume Sampling, the ray can only travel 1024 steps at .1 meters (BU) per step. In other words, the ray can only travel 1024*.1 = 102.4 meters before it must give up.

There are a couple ways to fix this.

Increase the max number of steps

This will keep everything as it is, but allow the rays to travel farther. It will likely increase rendertime however.



Increase the step size

This will make rays jump farther between steps and significantly speed up rendering, but may make the volume appear less detailed.

1024*.5 = 512 meters/BU, which is quite sufficient to traverse the whole of your domain. Note that details smaller than the step size may be "jumped over" by volume rays as they step along, essentially rendering the volume like those details were never there.



Use Equiangular sampling

Depending on your exact situation, you might find it's faster/less noisy to use Equiangular sampling for your volume. You'll have to experiment and see what works best in your scene.